Flavonoids are some of the most abundant and most studied bioactive components of plants with a wide range of therapeutic properties in humans. In recent years, public interest in the use of these compounds as supplements has rapidly increased worldwide. This popular science book is focused on the 15 most promising flavonoids, their physicochemical properties, discovery history, dietary sources, metabolism, and therapeutic activities. Unlike all other books on flavonoids published to date, the current book does not describe preclinical molecular studies and complicated cellular signaling mechanisms modulated by these phytochemicals, as these data cannot be directly extrapolated to in vivo conditions in the human body. Instead, this book touches the tip of the iceberg, discussing the results obtained from human studies, clinical trials, thereby providing the most relevant picture about the actual therapeutic roles of these compounds. This easy-to-read and systematically structured book is therefore intended for a wide audience—not only researchers and students but also the general readers who plan to use flavonoid-containing supplements to improve their health and well-being.